Module solana_ledger::erasure

Erasure Coding and Recovery

Shreds are logically grouped into erasure sets or blocks. Each set contains 16 sequential data shreds and 4 sequential coding shreds.

Coding shreds in each set starting from start_idx: For each erasure set: generate NUM_CODING coding_shreds. index the coding shreds from start_idx to start_idx + NUM_CODING - 1.

model of an erasure set, with top row being data shreds and second being coding |<======================= NUM_DATA ==============================>| |<==== NUM_CODING ===>| +—+ +—+ +—+ +—+ +—+ +—+ +—+ +—+ +—+ +—+ | D | | D | | D | | D | | D | | D | | D | | D | | D | | D | +—+ +—+ +—+ +—+ +—+ . . . +—+ +—+ +—+ +—+ +—+ | C | | C | | C | | C | | | | | | | | | | | | | +—+ +—+ +—+ +—+ +—+ +—+ +—+ +—+ +—+ +—+

shred structure for coding shreds

• —–– meta is set and used by transport, meta.size is actual length | of data in the byte array shred.data | | + – data is stuff shipped over the wire, and has an included | | header V V +–––––+————————————————————+ | meta | data | |+—+– |+—+—+—+—+——————————————+| || s | . || i | | f | s | || || i | . || n | i | l | i | || || z | . || d | d | a | z | shred.data(), or shred.data_mut() || || e | || e | | g | e | || |+—+– || x | | s | | || | |+—+—+—+—+——————————————+| +–––––+————————————————————+ | |<=== coding shred part for “coding” =======>| | | |<============== data shred part for “coding” ==============>|

Structs

ErasureConfig
Session	Represents an erasure “session” with a particular configuration and number of data and coding shreds

Constants

NUM_CODING	Number of coding shreds; also the maximum number that can go missing.
NUM_DATA	Number of data shreds